The present invention generally relates to liquid heating appliances, such as water heaters, and, in a preferred embodiment thereof, more particularly relates to protective apparatus used to prevent temperature and pressure-created bursting of tanks in which pressurized liquid is stored and heated.
There are many types of water heating appliances including gas, electric and oil fired water heaters, instantaneous water heaters, boilers, swimming pool heaters and the like, as well as various other types of liquid heating appliances. Such liquid heating appliances typically have a tank for holding liquid to be heated, and a heating system for heating the liquid to and maintaining it at a predetermined first heated temperature. With such liquid heating appliances the possibility exists of going into a heating “run-away” condition, if controls or safety devices fail, in which the temperature and pressure within the tank uncontrollably increase. If such temperature and pressure increases are not stopped, the tank can explode.
For this reason, liquid heating appliances of this general type are typically provided with a temperature and pressure relief valve which senses these increases and automatically opens to create a pressure relief passage, extending from the tank interior through the opened valve, that relieves the increasing pressure within the tank to prevent it from bursting. A temperature and pressure relief valve is normally based on opening a spring-loaded valve portion operated by a bimetal or equivalent rod activated by sensed temperature and/or pressure. The problem with these conventional types of temperature and pressure relief devices is that they are subject to failure due to scale build-up, corrosion, being plugged, leaking, being removed or not installed at all, etc. Failure of this conventional type of tank protective device for any reason leaves the tank susceptible to internal overpressurization and explosion. Accordingly, a need exists for liquid heating appliance overpressurization apparatus which eliminates or at least substantially reduces these problems associated with conventional temperature and pressure relief valves.